Stress corrosion cracking (SCC) susceptibility of a tempered martensite downhole tubular steel were evaluated in CO2 partial pressures from 500-3000 kPa and different strain rates from 5×10-7-2 ×10-6 S-1 at 175°C in carbonate-bicarbonate environments. Constant extension rate tests coupled with a high temperature/high pressure autoclave were used. Results revealed the occurrence of SCC at CO2 partial pressure from 500-1500 kPa. However, at CO2 partial pressures greater than 1500 kPa, SCC susceptibility decreased and uniform corrosion was observed without cracking. In addition, increasing strain rate decreased SCC susceptibility. Corrosion products and cracks distribution were analyzed by X-ray diffraction and scanning electron microscopy. The occurrence of SCC was attributed to the formation of protective corrosion products mainly iron carbonate layer on the surface.
The search for new oil and gas resources has forced the industry towards deeper, deviated wells and the use of extended reach drilling technology, horizontal wellbores and multiple lateral completions. Operational activities have moved toward harsher environments in deeper high pressure/high temperature wells and deep water for the exploration of new reserves of oil and gas. New project development and operations have faced increased challenges in which facilities integrity and accurate prediction of materials performance become important. Additionally, the economic incentive of multi-phase transportation through subsea completions and long infield flowlines causes increased risk of corrosion. As corrosion becomes a main operational hindrance to successful oil and gas production, management and control of corrosion becomes necessary for the cost effective design of facilities and their safe operations.1-2 Traditionally, carbon and low alloy steels are used for transportation pipelines as well as downhole tubing and casing. Even though these steels do not show appropriate performance for uniform CO2 corrosion, the industry still relies on the extended use of carbon and low alloy steels.
